Now, Merrick identifies this in the caption (which is quoted here in full):

'LEFT: Identification of III. Gruppe aircraft took two forms, both of which appeared at the same time, either as a vertical bar or as a horizontal 'sine wave' form. The Bf 109 F-4 trop in the background has the latter form of marking, in this instance its white colouring, plus the 'White 4' marking identify it as a 4. Staffel, III. Gruppe aircraft (possibly of JG 77). Note particularly the form of the '4' marking and compare it with the style of the 'White 3' marking on the Gruppen-Adjutant's Bf 109 G-2 trop, W.Nr. 10681. Both aircraft were camouflaged in standard 78/79 tropical finish, with a full array of North Africa tactical markings in white. (J. Crow).'

Now - something must have gone terribly wrong here - the 'White 4' would in my opinion identify an aircraft as belonging to the first Staffel of it's Gruppe. In this case the III. Gruppe as given by the wave behind the Balkenkreuz. So - at this stage of the war that would be the 7. Staffel of Jagdgeschwader X (presumably JG 77).

Also - I think the caption lacks in that it should probably say that the '<3 +' marked aircraft would indicate that the aircraft did probably not belong to III. Gruppe, but rather was an aircraft from either Geschwaderstab or I. Gruppe Stab as it had no additional marking behind the Balkenkreuz. It could of course also be a Gruppenstab aircraft of II. or III. Gruppe.

The fact that there is a difference in the shade of the '4' and '~' when compared to the white colour fo the Balkenkreuz and the tailband could also mean that the code on this aircraft could be yellow rather than white is also a point I would like to discuss, although it could be different types of paint used causing this.

Although I have yet to get a copy of Ken Merrick's latest publication and therefore cannot positively identify the photo in question, I have a distinct notion that it is part of a series of photos taken at Bir-el-Abd after this airfield was abandoned by the Luftwaffe in November 1942. Two images of this series can be seen on page 260 of Jagdfliegerverbände Vol. 8 / II. If this is not the case, please forget the following comment.

The identity of the two Messerschmitts in question has been ascertained for some time - the Bf 109 G-2 in the foreground, carrying the marking " white < 3 " belonged to Stab/JG 77 and was most likely the a/c with the WerkNr. 10 501. The markings identify this Bf 109 G as part of Stab/JG 77 which sported a single white chevron together with a small white numeral ( vide JFV 8/II, p. 269 ).

The Bf 109 F-4 trop in the background belonged to 9./JG 27; III./JG 27 was the only Bf 109 unit in North Africa to use the old wavy line as Gruppen-symbol so that there can be no doubt at all as to the "owner" of this a/c.

Thanks for the comment. This is one of the situations were a reader has a real problem, the photograph as reprinted in the book is just not good enough to make the WNr of the aircraft in question readable. And as Merrick has identified it as WNr 10681, this is what we would be looking for in our databases. And as You might suspect, I have not found a correspondance in my database for the mentioned WNr and a Stab aircraft for JG 77 or JG 27.